1. Field of the Invention
The present invention relates to a valve actuating apparatus for resting the operation of a valve such as intake and exhaust valves in an internal combustion engine. More particularly, it relates to a valve actuating apparatus which can render only a predetermined intake and/or exhaust valve or valves inoperative at a given engine condition.
2. Description of the Related Art
In a multi-cylinder internal combustion engine, it is known to selectively render only predetermined intake or exhaust valve(s) inoperative in order to cancel out the associated cylinder(s), thereby controlling the total displacement of the effective cylinders, in accordance with the engine load, resulting in the realization of a variable-cylinder internal combustion engine.
Among known valve actuating apparatuses of the kind mentioned above, those closest to the present invention are disclosed, for example, in Japanese Unexamined Utility Model Publication (Kokai) Nos. 59-68109 and 59-67506, in which a rocker arm is composed of two arm elements interconnected by a connecting pin so as to be foldable, with the outer ends of the respective arm elements engaged with the rocker shaft and the valve stem, respectivily. A further pin is secured on a stationary bracket and can be inserted into a hole arranged coaxially of the connecting pin. When the further pin secured on the stationary bracket is inserted in this hole, this pin provides a fixed pivot shaft about which only one arm element moves to operate the valve. When the further pin is removed from the hole, the rocker arm is foldable about the connecting pin to absorb the cam lift. In this prior art system, only one arm element extends between the valve stem and the connecting pin so as to have a length sufficient to actually operate the valve, and the other arm element is further extended from that sufficient length of the one arm element.
Japanese Utility Model Application Nos. 59-120916 and 59-153107, filed by the same assignee as for the present case, discloses a valve actuating apparatus for optionally resting the operation of a valve in an internal combustion engine, including a foldable rocker arm. This rocker arm comprises two arms rotatably interconnected by a connecting pin extending in parallel to a rocker shaft, and a lock pin which detachably interconnects the two arms. The connecting pin and the locking pin occupy separate positions from each other, so that the two arms are brought together as an integral rocker arm to operate the valve when the lock pin interconnects the two arms. The two arms are foldable at the connecting pin to absorb the lift of the cam and thus rest the operation of the valve.
In the rocker arm described above, when the rocker arm is in the foldable condition, it is folded down by contact with a cam nose portion of the cam, and returned to a generally straight original contour by a return spring when coming into contact with a base circle portion of the cam, this folding cycle being repeated. However, due to a tappet clearance normally provided in the intake or exhaust valve, there is a tendency for the rocker arm to be returned by the return spring beyond the above-mentioned generally straight original contour. The design of this apparatus is such that, upon the change from the foldable condition to the integral condition by the actuation of the lock pin, the lock pin can enter the corresponding cylinder to interconnect the two arms when the rocker arms assumes that generally straight original contour while it is in contact with the base circle portion of the cam. However, the rocker arm is returned to a point beyond this original contour, the lock pin may fail to enter the cylinder.